This proposal will study a recently recognized form of hearing disorder called auditory neuropathy (AN). Different from cochlear damage, AN is characterized by normal measures of cochlear outer hair cells but abnormal measures of the central auditory pathway beginning with auditory nerve. The hearing disorder typically affects speech comprehension out-of-proportion to the pure tone loss, particularly speech recognition in noise. AN is not rare and accounts for 10 percent of newborns identified as having hearing loss. The disorder occurs in children and adults. In adults the disorder is commonly associated with a peripheral neuropathy. Loss of neural synchrony is proposed as a cardinal mechanism underlying the hearing disorder. The sites of abnormality in AN could include auditory nerve and/or inner hair cells and their synapses with auditory nerve dendrites. Our long-term goals are to understand the AN mechanisms and functions in order to provide a scientific basis for alleviating the hearing deficit in AN subjects. We propose three experiments using both psychophysical and elecrophysiological techniques to characterize: (1) fundamental and complex auditory processes in AN subjects in order to explain their speech recognition difficulty, particularly in noise; (2) distinguish between the site of the disorder as being at auditory nerve or at inner hair cell/synapse complex; and (3) optimize signal processing for AN subjects with cochlear implants. The resultsof our studies could have major impact on the diagnosis, classification, and treatment of auditory neuropathy.